The grey, gravel type of cat litter should never be used but if it's wood based stuff then you may be able to use it - I was looking at Alan Francis' garter snake site earlier and he says on there about using a "compressed sawdust based cat litter" so some types must be ok.
You'd have to be careful that it doesn't contain any kind of deodorising agent or any other added ingredients, and as markhill has said it'll be very drying, so could cause shedding problems, and more than likely pretty dusty.
Also, pricewise, beech chip, aspen and hemp would surely be cheaper if bought in a decent quantity.
Personally I wouldn't bother with it - there's plenty of other tried and tested options out there.
I hate that stuff. I tried it before but when it gets wet - and lets face it, a snake makes a f*ckin mess when it goes in and out of the water bowl - it dries as a dust, and is nasty, the stuff got up my nose when I cleaned them out so I hate to think what it would be doing to the snake, I took it out after 3 days :? :lol: